Scientists wanted to know why a particular gene kept coming up in studies related to both addiction and obesity. The connection? Impulsivity. But only for men.

Researchers at the University of Nebraska took cheek swabs from 439 white, college-age volunteers (only Caucasians to eliminate race-based genetic differences). They completed questionnaires about their personality, and use of alcohol, tobacco and other drugs. The scientists also gave them a patience and impulsivity test by asking them to estimate how long it took them to complete a particular task.

Their results, which will be published in the November 19 issue of Drug and Alcohol Dependence, found that men with a certain variant of a gene called NRXN3 were impulsive and tended to have addiction problems. NRXN3 has been associated with cigarette, alcohol, and opiate addiction, as well as what seemed like a bit of a wildcard: obesity. But now they believe the impulsive consumption of drugs, alcohol or food is what kicks off the addiction and obesity.

This of course doesn't mean that if you have the gene variant you're doomed to a life of sitting in a dark room getting drunk and smoking cigarettes as you bust out of your jeans (as fun as that may sound). The gene puts you at risk, so if you're triggered by environmental factors like peers, family or psychiatric disorders, you're more likely to have problems. Genetic testing company 23andMe estimates that the heritability of alcohol dependence is between 38 and 64 percent.

Scott Stoltenberg, the University of Nebraska psychologist who led the study put it this way:

You almost can't paint a complicated enough picture of how genes are associated with behaviors. There are a lot of factors out there that influence our behaviors, and genes are just one of them.

Other genes have been associated with everything from impulsive, violent behavior in Finnish men to a tendency toward promiscuity and a love of horror films. Still, know that you can't go around blaming your genes alone for black out nights of cocaine-fueled Bioshock marathons.

P.S. They don't know why they only saw the association in men. [LiveScience]